The present invention relates to a dot recording device, such as a serial printer, and more particularly, to a dot recording device including a record medium regulating part and dot recording head in opposed facing relationship, the dot recording device for recording on a record medium that is carried on the record medium regulating part.
With printers, such as serial printers, that have a dot recording head formed to scan a printing medium (e.g., the surface of a paper sheet) along a raster, the recording head is provided with a dot formation element array made up of multiple dot formation elements arrayed in a sub scanning direction on the head surface. Multiple scanning lines of the same color can be simultaneously printed by the dot formation element array with one pass along the main scanning path. As used herein, recording, and derivatives thereof, indicate printing, and derivatives thereof.
In a printer using such a recording head, particularly an ink-jet printer, differences in characteristics of individual ink-jet nozzles (an ink-jet nozzle is equivalent to the dot formation element discussed above) and differences in pitch between ink-jet nozzles are obstacles to realizing printing of high quality images.
U.S. Pat. Nos. 4,198,642 and 5,844,585 disclose a printing method referred to as "interlace recording" in which printing of high quality images is enabled by dispersing variations in the characteristics and pitch of ink-jet nozzles on a printed image.
With interlace recording, a recording head is provided with a nozzle array in which N number of ink-jet nozzles are arrayed in a sub scanning direction at a nozzle pitch k equivalent to k times the dot pitch (k-dot pitch). Nozzle pitch is a function of recording (printing) resolution, which can be measured in dpi. For N number of nozzles, the nozzle pitch k is N or an integer smaller than N. Every time the nozzle array finishes one main scanning path, the print medium is advanced (i.e., sub scanning) a fixed distance equivalent to N times the dot pitch (N-dot pitch).
An illustrative example of the interlace recording method is described below. It is assumed that a nozzle array is provided with 20 (N=20) nozzles arranged at 3-dot pitch (k) to generate an image resolution of 360 dpi. Thus, the one-dot pitch is equivalent to 1/360 inch, with the pitch between nozzles being 3/360 inches--the equivalent of 3 (k) times the one-dot pitch. Also, the distance of sub scanning (equal to the field distance the print medium is advanced after the nozzle array completes one main scanning path) is 20/360 inches which is equivalent to 20 (N) times the one-dot pitch.
As each nozzle is moved by 20/360 inch when sub scanning is executed, the nozzles are initially moved with each nozzle being moving beyond 7 nozzle positions (nozzle pitches), that is, moving into an advanced position by one-dot pitch ahead of 21/360 inches. With further sub scanning, each nozzle is moved by 2-dot pitches from the advanced position to a nozzle position ahead of 14 nozzles (14 nozzle pitches). Consequently, when each line is printed by each nozzle in a main scanning path at a certain time, in the subsequent scanning path, an adjacent line is printed by a nozzle moved from 7 nozzle positions away, and in the further subsequent main scanning path, the next adjacent line is printed by a nozzle moved from 14 nozzle positions away.
As described above, in printing according to the interlace recording method, adjacent lines are necessarily printed by different nozzles. As a result, even if there are slight differences in the characteristics of an individual nozzle and pitch, the differences become obscured on a printed image and a printed image of high quality is acquired.
As described above, the interlace recording method may enable printing of high quality images. However, if the interlace recording method is used for printing and started by using all of the nozzles, an area (hereinafter called an "incomplete printed area") is defined at the front end of a record medium in which a line cannot be completely precisely printed using the method. In addition, assuming that a nozzle located at the front end of the recording head in the downstream side in the paper carrying direction is No. 1 and a nozzle located at the rear end of the recording head, on the upstream side is No. N, then printing using all nozzles from Nos. 1 to N cannot be executed when printing is started and only nozzles after a nozzle No. T located between the nozzle No. 1 and the nozzle No. N can be used (driven) when printing is started. However, the nozzle No. T approaches the nozzle No. 1 with every sub scanning. As used herein, "downstream" refers to the direction of paper movement as it passes through the apparatus, and "upstream" is the opposite direction of downstream.
To realize printing of high quality images according to the interlace recording method, the distance between printing paper and the nozzle array, a so-called paper gap, should be held fixed during printing. Therefore, a record medium regulating part is provided in the printing apparatus disposed opposite to the recording head. The paper gap is defined by supporting the paper from the bottom on the flat top face of the record medium regulating part. In a conventional record medium regulating part, the flat top face is provided downstream of the nozzle array (in the sub scanning direction).
The conventional record medium regulating part is composed of a plurality of spaced-apart pieces not linearly arranged in the main scanning direction. Where printing is executed by ink that contains moisture, such as ink-jet printer ink, a slightly wavy phenomenon, known as a "cockling phenomenon", occurs because paper is extended and deformed because of moisture penetration from the ink. The above separated record-medium-regulating-part structure facilitates extinguishing the extension of paper by the above cockling phenomenon between top faces of adjacent pieces.
To hold the above paper gap fixed when printing is started, the front end of paper is made to reach the top face of the record medium regulating part. However, as the flat top face of the record medium regulating part is provided on the downstream side outside a range of the nozzle array, the front end of the paper is located outside the range of the nozzle array with the front end of the paper reaching the top face of the record medium regulating part. Therefore, a range at the front end of the paper cannot be printed upon (the part at the front end of the paper which is downstream of and not opposite to the nozzle array).
Further, as described above, the interlace recording method cannot use all nozzles when printing is started; that is, the nozzles No. 1 to No. T are not aligned with and cannot be initially used.
Recently, a recording device has become desired capable of generating images of high quality, including photograph image quality, which can print with a reduced margin at the upper end of a record medium. As described above, prior art devices have structural limitations which do not permit reducing the margin at the upper end of a record medium.
Heretofore, and referring to the discussion above, Japanese published unexamined patent application No. Hei9-71009, discloses a method for printing a main scanning line in the area including the nozzles No. 1 to No. T. Specifically, a printing method is disclosed wherein an interval of sub scanning (the quantity of a paper feed) is reduced at the start of printing, as compared with the fixed interval of sub scanning in a conventional interlace recording method. A portion of the nozzles on the front end side of the recording head is used to perform the initial printing. According to this printing method, a conventional type interlace recording method is also used. A range which previously could not be printed can be reduced and a margin at the upper end of the printing record can be reduced. However, the method requires two separate printing methods (one at the start of printing and the interlace recording method adopted afterward) which must be switched, resulting in a complicated driving controller.